Hi Jackie,
As long as you do not overwrite the formulas, then any new data will not
affect the formula.  I suspect though that there is more to this question.

Are you concerned about writing new data into a cell that has a formula in
it?  The way to stop a cell's data being overwritten is to put protection
onto it.  This means taking protection off all the other cells otherwise you
will not be able to write data to any cell.

First select the whole worksheet concerned, then go to Format\Cells and
select the protection tab and unselect the 'locked' tick box, then select the
cells with the formula you want to protect and go back to
Format\Cells\Protection and select the locked box.  This now has set only
those cells that you want to protect able to be protected.  All the other
cells will now be unprotected.  To go to Tools\Protection\Protect sheet and
that will provide you with options to complete.  Leave the tick in the box
"protect worksheet..." and assign a password that will allow the protection
to be removed if and when you need to access those secured cells.

Now you should be able to write to all but the cells containg the formula.

Hope this is what you were after.

Regards

DavidC